Temperature measurement and override control for turbojet engines



April 24, 1956 D. R. DE BOISBLANC 2,742,756

TEMPERATURE MEASUREMENT AND OVERRIDE CONTROL FOR TURBOJET ENGINES Filed June 4, 1951 27 TEMPERATURE INDICATOR MAIN FUEL CONTROL SERVO MECHANISM AMPLIFIER THRESHOLD DEVICE AUTOMATIC OVER-RIDING F'UEL CONTROL FIG. 1

INVENTOR. D. R. DE BOISBLANC FIG. 2.

A T TORNEYS l l l TEMPERATURE MEASUREMENT AND OVERRIDE CONTROL FOR TURBOJET ENGHWES Deslonde R. de Boisblanc, Bartlesvilie, Okla assignor to Phillips Petroleum Company, a corporation of Betaware Application June 4, 1951, Serial No. 229,788

11 Claims. (Cl. Gil -35.6)

This invention relates to a combination thermocouple and flame detector. In another aspect, it relates to a control system for detecting the presence of flame in the mixing chamber between the turbine and flame holder of a turbojet engine, with control mechanism for adjusting the engine fuel supply so as to prevent the occurrence of such flame.

In turbojet engines, air is compressed, and passed to a combustion chamber where it is mixed with fuel, the resultant combustion increasing the temperature to a high value. The products of combustion then pass through a turbine, which has a driving connection with the compressor, after which they are ejected through an outlet nozzle, then reaction of the air as it leaves the nozzle producing a forward propulsive thrust. In many such engines, additional fuel is mixed with the gases from the combustion chamber after they leave the turbine, the mixture then passing through a gridlike structure to a second combustion chamber where further burning takes place. The function of the gridlike flame holder is to reduce the velocity of a portion of the mixture to such an extent that combustion can be supported downstream of the flame holder.

If the supply of fuel to the secondary mixing zone is excessive, flashback may occur. That is, flame may be present in the secondary mixing chamber upstream of the flame holder.

It is an object of this invention to prevent the occurrence of this undesirable condition by positioning a flame detector in the secondary mixing chamber which actuates suitable control mechanism to regulate the fuel supply so as to prevent flashback.

It is a further object to provide a flame detector which embodies a thermocouple so that temperature can be measured in the secondary combustion chamber as well as the presence or absence of flame therein.

It is a further object to provide apparatus which is simple in construction, reliable in operation, and economical to manufacture and use.

Various other objects, advantages and features of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawing, in which:

Figure l is a sectional view of the downstream portion of a turbojet engine with certain circuit elements of this invention indicated in block diagram; and

Figure 2 is a vertical sectional view of the novel combination flame detector and thermocouple.

Referring now to the drawing in detail, the downstream portion of the turbojet engine includes a generally cylindrical tube having, at its end, a tapered discharge nozzle 11. The engine incorporates a compressor, not shown, driven by a shaft 12 together with a series of combustion chambers, two of which are indicated at 13, wherein the compressed air is admixed with fuel and burned. The products of combustion discharged from the chambers 13 impinge upon the blades 14 of a turbine 15 which drives the compressor through shaft 12.

2,742,756 Patented Apr. 24, 1956 After leaving the turbine, the hot products of combustion enter a secondary mixing chamber 16 which is provided with a diffuser cone 17. Secondary fuel is supplied to the mixing chamber 16 through a ring of nozzles 18 connected to a common fuel supply line 19. In this manner, the products of combustion are mixed with secondary fuel in the chamber 16 and, thence, pass through a flame holder 20 to a secondary combustion chamber 21. The flame holder consists of a set of small cones 22 supported by a latticework, not shown. The velocity of the combustible mixture passing through the cones from mixing chamber 16 to combustion chamber 21 is substantially reduced so that combustion can occur and is supported within the cones and the secondary combustion chamber 21, it being understood that the velocity of the gases in mixing chamber 16 is too high to support combustion. From the chamber 21, the combustion gases are ejected through the tapered nozzle 11, the reaction of the gases leaving the nozzle producing a forward propulsive thrust.

In accordance with the invention, a combination flame detector and thermocouple 23 is supported by the shell 10 and protrudes into mixing chamber 16 at a position between the turbine 15 and flame holder 20. A pair of leads 25 and 26 connect the thermocouple portion of the unit 23 with a temperature indicator 27 so as to provide a continuous indication of the temperature within the mixing chamber 16. Leads 26 and 28 extend from the flame detector portion of the unit 23 to a threshold device 29, the output of which is fed through an amplifier 30 and, thence, to an automatic overriding fuel control 31 operatively connected to a valve 32 in the fuel line 19, the valve 32 normally being actuated by a manual fuel control 33.

When flashback occurs, a flame appears within the mixing chamber 16 with the result that an electrical output is produced by the flame detector portion of the unit 23. This signal is amplified by unit 30 and actuates automatic fuel control 31 so as to reduce the amount of fuel supplied to nozzles 18 from line 19 until the flashback condition is eliminated and flame is no longer present within the mixing chamber 16. When the flashback condition is eliminated, control of the fuel supply reverts to the manual fuel control unit 33. The overriding feature of the controls 31, 33 may be provided in any suitable manner familiar to those skilled in the art. For example, fuel control 31 may actuate a separate valve in the fuel line which is biased to an open position, at which it has no eifect upon the quantity of fuel passing through line 19. When unit 31 is actuated by a signal from flame detector unit 23, the valve is closed to the extent necessary to relieve the undesirable flashback condition. When the condition is eliminated, no output is supplied to unit 31 and the separate valve returns to its fully open position, thus permitting the fuel supply to be controlled by unit 33. A suitable valve control is shown in Telemetering, Borden and Thynell, page 181, Reinhold Publishing Corporation (1948). The valve shown in Figure can be in the fuel line, and the flow meter receiver can be actuated by signals from the amplifier 30 of Figure 1 so as to control the fuel valve in the manner described.

The function of threshold device 29 is to permit the passage of signals of greater than a predetermined amplitude to the amplifier 30 with elimination of signals of less than such predetermined amplitude. This device may generally be a biased diode of the type shown in my Patent No. 2,448,323, entitled Detonation Meter. The threshold level is so adjusted that any random voltages produced by detector 23 when no flame is present in the chamber 16 are not of suflicient amplitude as to pass through the device 29 and actuate amplifier 30. However, when a flame impinges upon the detector 23, the

amplitude ofthe signal is such that it passes through threshold device 29 and amplifier-30 with resultant actuation of fuel control 31. Although it is usually preferable to utilize the device 29, it is not an essential feature of the invention and may, in some cases, be eliminated.

The construction of the unit 23 is shown in detail by Figure 2. In a preferred modification of the invention,- the detector includes a ceramic generally hemispherical tip 35 formed from a suitable ceramic material, such as alundum cement. This material is made by fusing alumina in electric furnace, the resulting material, being ground up and, if desired, admixed with suitable fluxing agents such as magnesium oxide. The tip 35-is secured to and supported by a cylindrical member '36, preferably formed from stainless steel, the tube having'a plurality of holes 37 circumferentially spaced about its outer end through which protrude portions of the ceramic tip 35 to secure the parts in assembled relation. Mounted within the tube 36 is a cylindrical insert 38 of refractory insulating material, this insert being provided with a pair of spaced longitudinal passages 39, 40, the end of the insert engaging the flat inner surface 41 of the tip 35.

A thermocouple junction 42 is embedded within the ceramic tip 35, the leads 25, 26 extending through the respective passages 39, 40 and the ceramic tip 35 to the thermocouple junction. As a result, a potential appears across leads 25, 26 which is representative of the temperature at the thermocouple junction 42. This potential may be fed to the indicator 27 or, alternatively, through servomechanism 27a to main fuel control 271) to reduce the supply of fuel to the main burner, not shown, when the temperature becomes excessive at the thermocouple junction. The lead 28 is directly connected to the metal tube 36, and lead 26 is in electrical contact with the material forming the ceramic tip 35. When a flame impinges upon the ceramic tip, ions present in the flame bombard the surface of the tip and the electrical charges carried by the ions cause a current flow in. the ceramic. material until the charges are dissipated and all points in the ceramic medium are at the same potential. Accordingly, an electrical output is produced between leads 26, 28 when flashback occurs in the mixing chamber 16 with resultant incidence of a flame upon the ceramic tip 35. This electrical output, as previously explained, actuates automatic fuel control 31 through threshold device 29 and amplifier 3t) so as to decrease the fuel supply to burners 18 until the undesirable flashback. condition is eliminated.

While the invention has been described in connection with a present, preferred embodiment thereof, it is to,

be understood that this description is illustrative only.

and is not intended to limit the invention, the scope of which is defined by the appended claims.

I claim:

I. The combination, with a reaction motor having a secondary combustion chamber, a flame holder upstream from said secondary combustion chamber, a mixing chamber upstream from said flame holder, and fuel injection means disposed in said mixing chamber; of a combined flame detector and thermocouple positioned in said mixing chamber, said flame detector having an electrical output of a characteristic value when a flame is incident thereon, means controlled by said flame detector to decrease automatically the amount of fuel supplied to said injection means when the flame detector output assumes said characteristic value, temperature indicating means, fuel control means, and means operatively connecting said thermocouple with said temperature indicating and fuel control means.

2. The combination, with a reaction motor having a secondary combustion chamber, a flame holder upstream from said secondary combustion chamber, a mixing chamber upstream from said flame holder, and fuel injection means disposed in said mixing chamber; of a combination thermocouple and flame detector comprising a ceramic member positioned in said mixing chamber downstream of said fuel injection means, leads conthermocouple junction within said ceramic material, a

temperature indicator, and leads connecting said thermocouple junction with said temperature indicator, whereby the temperature of the mixing chamber can be deter mined.

3. The combination, with a reaction motor of the turbojet type having a turbine, fuel supply nozzles downstream from said turbine and a flame holder downstreamfrom said fuel injection means; of a flame detector positioned between said turbine and said flame holder, said detector incorporating a generally hemispherical piece of ceramic material, a thermocouple embedded insaid ceramic material, a temperature indicating device, a pair of leads connecting said thermocouple to said indicatingdevice, one of said leads being in electrical contactwith said ceramic material, a third lead connected to a circumferential point on said piece of ceramic material, an amplifier having an input circuit connected to said one lead and said third lead, and an automatic fuel control responsive to the output of said amplifier to decrease automatically the amount of fuel supplied-to said fuel nozzles whenthe' electrical output between said one lead and said third lead rises above a predetermined value.

turbojet type having a secondary combustion chamber, a flame holder upstream from said secondary combustion chamber, a mixing chamber upstream from said flame holder, and fuel injection means disposed in said mixing chamber; of a flame detector comprising a ceramic member positioned in said mixing chamber downstream of said fuel injection means, leads connected to spaced points on said ceramic member, whereby an electrical signal is generated between said leads when a flame contacts said member, a threshold device having an input circuit connected to said leads, said device passing only signals of greater than a predetermined amplitude, an amplifier fed by said threshold device, and means controlled by said amplifier to decrease automatically the amount of fuel supplied to said injection means when.

the electrical signal from said flame detector is of suflicient amplitude to pass said threshold device.

5. The combination, with a reaction motor of the turbojet type having a secondary combustion chamber,

a flame holder upstream from said secondary combustion chamber, a mixing chamber upstream from said flame holder, and fuel injection means disposed in said mixing:

chamber; of a flame detector positioned in said mixing chamber incorporating a generally hemispherical piece of ceramic material, a thermocouple embedded in said ceramic material, a temperature indicating device, a pair of leads connecting said thermocouple to said indicating device, one of said leads being in electrical contact with said ceramic material, a third lead connected to a circumferential point on said piece of ceramic material, a threshold device having an input circuit connected to said one lead and said third lead, said threshold device passing only signals of greater than a predetermined amplitude, an amplifier fed by said threshold device, and an automatic fuel control responsive to the output of said amplifier to, decrease automatically the amount of fuel supplied to said injection means when the electrical output between said one lead and said third lead rises above said predetermined amplitude.

6. The combination, with a reaction motor of the turbojet type having a secondary combustion chamber, a flame holder upstream from said secondary combustion chamber, a mixing chamber upstream from said flame holder, and fuel injection means disposed in said mixing chamber; of a flame detector comprising a ceramic member positioned in said mixing chamber downstream of said fuel injection means, leads connected to spaced points on said ceramic member, whereby a characteristic electrical output is produced between said leads when a flame is incident upon said member, a threshold device having an input circuit connected to said leads, said device passing only electrical detector outputs of greater than a predetermined amplitude, an amplifier fed by said threshold device, and means controlled by said amplifier to decrease automatically the amount of fuel supplied to said injection means when the electrical output of the detector rises above said predetermined amplitude.

7. The combination, with a reaction motor of the turbojet type having a secondary combustion chamber, a flame holder upstream from said secondary combustion chamber, a mixing chamber upstream from said flame holder, and fuel injection means disposed in said mixing chamber, of a flame detector positioned in said mixing chamber incorporating a generally hemispherical piece of ceramic material, a thermocouple embedded in said ceramic material, a main fuel control, a servomechanism communicating with said main fuel control to reduce the fuel it supplies when the thermocouple temperature becomes excessive, a pair of leads connecting said thermocouple through said servomechanism to said main fuel con- 'trol to transmit a signal thereto, one of said leads being in electrical contact with said ceramic material, a third lead connected to a circumferential point on said piece of ceramic material, a threshold device having an input circuit connected to said one lead and said third lead, said threshold device passing only signals of greater than a predetermined amplitude, an amplifier fed by said threshold device, and an automatic fuel control responsive to the output of said amplifier to decrease automatically the amount of fuel supplied to said injection means when the electrical output between said one lead and said third lead rises above said predetermined amplitude.

8. The combination, with a reaction motor of the turbojet type having a secondary combustion chamber, a flame holder upstream from said secondary combustion chamber, a mixing chamber upstream from said flame holder, and fuel injection means disposed in said mixing chamber, of a flame detector positioned in said mixing chamber incorporating a piece of ceramic material, a thermocouple embedded in said ceramic material, a main fuel control, a servomechanism communicating with said main fuel control to reduce the fuel supplied by said main control when the thermocouple temperature becomes excessive, a pair of leads connecting said thermocouple to said main fuel control to transmit a signal thereto, one of said leads being in electrical contact with said ceramic material, a third lead connected to a circumferential point on said piece of ceramic material, a threshold device having an input circuit connected to said one lead and said third lead, said threshold device passing only signals of greater than a predetermined amplitude, an amplifierfed by said threshold device, and an automatic fuel control responsive to the output of said amplifier to decrease the amount of fuel supplied to said injection means when the electrical output between said one lead and said third lead rises above said predetermined amplitude.

9. A combination thermocouple and flame detector comprising a generally cylindrical conductive support, 'a solid generally hemispherical member of ceramic material secured to one end of said support, a thermocouple junction imbedded in said ceramic material, leads extending through said support and said member to said thermocouple junction, one of said leads electrically contacting said ceramic material, the potential across said leads indicating the temperature at the thermocouple junction, another lead connected to said ceramic material at a point spaced from the point of contact of said one lead with said ceramic material, whereby when a flame contacts said ceramic tip a current flows between said spaced points and in the leads connected to said spaced points.

10. A combination thermocouple and flame detector which comprises a metal tube having a plurality of circumferentially spaced openings adjacent one end thereof, a solid rounded tip of ceramic material secured to one end of said tube, said tip having portions thereof protruding through said openings, a generally cylindrical insert mounted within said tube and engaging the inner edge of said tip, said insert having a pair of spaced longitudinal passages formed therein, a thermocouple imbedded in said tip, leads extending through said passages to the respective terminals of said thermocouple junction, at least one of said leads being in electrical contact with said ceramic material, the temperature at the thermocouple junction generating a signal in said lead, and a third lead connected to said ceramic material at a point spaced from the point of contact of said one lead with said ceramic material, whereby when a flame contacts said ceramic tip a current flows between said spaced points and in the two leads connected to said spaced points.

11. Apparatus of claim 10 wherein the ceramic material is aluminum cement and the support is formed from stainless steel.

References Cited in the file of this patent UNITED STATES PATENTS Switzerland Feb. 16, 1951 

1. THE COMBINATION, WITH A REACTION MOTOR HAVING A SECONDARY COMBUSTION CHAMBER, A FLAME HOLDER UPSTREAM FROM SAID SECONDARY COMBUSTION CHAMBER, A MIXING CHAMBER UPSTREAM FROM SAID FLAME HOLDER, AND FUEL INJECTION MEANS DISPOSED IN SAID MIXING CHAMBER; OF A COMBINED FLAME DETECTOR AND THERMOCOUPLE POSITIONED IN SAID MIXING CHAMBER, SAID FLAME DETECTOR HAVING AN ELECTRICAL OUTPUT OF A CHARACTERISTIC VALUE WHEN A FLAME IS INCIDENT THEREON, MEANS CONTROLLED BY SAID FLAME DETECTOR TO DECREASE AUTOMATICALLY THE AMOUNT OF FUEL SUPPLIED TO SAID INJECTION MEANS WHEN THE FLAME DETECTOR OUTPUT ASSUMES SAID CHARACTERISTIC VALUE, TEMPERATURE INDICATING MEANS, FUEL CONTROL MEANS, AND MEANS OPERATIVELY CONNECTING SAID THERMOCOUPLE WITH SAID TEMPERATURE INDICATING AND FUEL CONTROL MEANS.
 9. A COMBINATION THERMOCOUPLE AND FLAME DETECTOR COMPRISING A GENERALLY CYLINDRICAL CONDUCTIVE SUPPORT, A SOLID GENERALLY HEMISPHERICAL MEMBER OF CERAMIC MATERIAL SECURED TO ONE END OF SAID SUPPORT, A THERMOCOUPLE JUNCTION IMBEDDED IN SAID CERAMIC MATERIAL, LEADS EXTENDING THROUGH SAID SUPPORT AND SAID MEMBER TO SAID THERMOCOUPLE JUNCTION, ONE OF SAID LEADS ELECTRICALLY CONTACTING SAID CERAMIC MATERIAL, THE POTENTIAL ACROSS SAID LEADS INDICATING THE TEMPERATURE AT THE THERMOCOUPLE JUNCTION, ANOTHER LEAD CONNECTED TO SAID CERAMIC MATERIAL AT A POINT SPACED FROM THE POINT OF CONTACT OF SAID ONE LEAD WITH SAID CERAMIC MATERIAL, WHEREBY WHEN A FLAME CONTACTS SAID CERAMIC TIP A CURRENT FLOWS BETWEEN SAID SPACED POINTS AND IN THE LEADS CONNECTED TO SAID SPACED POINTS. 